CODEWITHSUNDEEP
javasorting
Deepak_Sharma
Deepak_Sharma

Reputation: 61

Sorting HashSet

I have written a program to insert data in a HashSet...here is the code

public class Person implements Comparable<Person>
{
    private int person_id;
    private String person_name;
    public Person(int person_id,String person_name)
    {
        this.person_id=person_id;
        this.person_name=person_name;
    }
    /* getter and setter method */
    public boolean equals(Object obj)
    {
        Person p=(Person)obj;
        if(!(p instanceof Person))
        {
            return false;
        }
        else if(this.person_id==p.person_id)
            return true;
        else
            return false;
    }
    @Override
    public int hashCode()
    {
        return person_id*6;
    }
    @Override
    public int compareTo(Person o)
    {
        if(this.person_id>o.person_id)
            return 1 ;
        else if(this.person_id<o.person_id)
            return -1;
        else return 0;
    }
}

I havent pasted other two classes.All i am doing in those classes is populating the data and other is main class.

Now i understand that through Java Doc Api i came to know that there is method called sort() in Collections class.Now the issue which i am is that sort mathod takes list.

here is signature from doc sort(List list). I am facing problem to sort my hashset .Somebody told me to convert HashSet into TreeSet(Thats also mentioned in one of the thread is stackoverflow)...Is this the only way

Upvotes: 2

Views: 9875

Answers (2)

user2340939
user2340939

Reputation: 1981

Use LinkedHashSet instead, as It insert elements in a sorted manner, so the set is always sorted.

See http://docs.oracle.com/javase/7/docs/api/java/util/LinkedHashSet.html more information:

Hash table and linked list implementation of the Set interface, with predictable iteration order. This implementation differs from HashSet in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is the order in which elements were inserted into the set (insertion-order). Note that insertion order is not affected if an element is re-inserted into the set. (An element e is reinserted into a set s if s.add(e) is invoked when s.contains(e) would return true immediately prior to the invocation.)

Upvotes: 0

luiges90
luiges90

Reputation: 4598

Pretty much the only way. HashSet was never meant to be sorted. It does not keep any ordering of your items, in exchange for performance of contains, add and remove operations.

http://docs.oracle.com/javase/6/docs/api/java/util/HashSet.html

This class implements the Set interface, backed by a hash table (actually a HashMap instance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the null element.

So, just use TreeSet which keeps the sorting according to your class' natural ordering. I see your class implements Comparable which makes it readily be used in a TreeSet

Upvotes: 9

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